Atomic layer deposition (ALD) is a thin film deposition method that allows for the deposition of films having thicknesses on the order of nanometers in a precisely controlled way. Typically, ALD uses two or more gaseous precursors that are alternately and repeatedly applied to a substrate. A series of sequential steps in which a surface of the substrate is exposed to all precursors is called a deposition cycle. Each deposition cycle grows a single monolayer of film, or a fraction of a monolayer. This is due to the fact that in ALD the film growth depends on chemisorption, a process whereby a precursor molecule adheres to a substrate's surface through the formation of a chemical bond without further thermal decomposition of the precursor molecule taking place. Chemisorption stops naturally when all substrate surface sites available for chemical bonding with a precursor have been covered. Exposing the substrate to the second precursor results in a chemical reaction of the second precursor with the chemisorbed first precursor under the formation of a solid film, until all of the chemisorbed first precursor has been reacted and the substrate is covered with a layer of chemisorbed second precursor in a self-limiting manner. Consequently, ALD is a self-limiting layer-by-layer deposition method that offers highly conformal coating and excellent thickness control. These characteristics make it a method of interest to various industries, among which in particular the semiconductor, and more specifically, the solar cell industry.
In the solar cell industry, ALD may be used to deposit aluminum oxide (Al2O3) films for the passivation of advanced mono-Si solar cells. To this end typical film thicknesses of 5-15 nm are required, which can be achieved using traditional single or multi-wafer ALD systems. Currently, the throughput of the most efficient multi-wafer ALD systems at said film thickness is about 60 wafers per hour. The amount of surface area to be treated in order to obtain—for example—a solar cell panel for use on a rooftop, is considerable however. And with the demand for solar cell panels on the rise, there is an increasing need for ALD apparatus featuring a higher throughput.
The above-described ALD application is exemplary, and merely one of many in which the continual pressure within the semiconductor industry and related industries, such as solar cell industry or flat panel display industry, for an increased throughput is felt. It is therefore on object of the present invention to provide a device and a method for atomic layer deposition offering a much improved throughput capacity.